Article ID: JJID.2018.277
Increase of antimicrobial-resistant (AMR) bacteria caused by antimicrobial usage is a public health problem. We investigated the proportion of cephalexin (LEX)-resistant bacteria in fresh feces obtained from antimicrobial-free broilers in three flocks at <15, 15-40, and >40 days of age. DHL agar plates containing 25 μg/mL LEX (DHL-L) showed LEX-resistant bacteria in all flocks at <15 days of age and in one flock at >40 days of age. The bacterial counts on DHL and DHL-L were 105-108 colony forming units (CFU)/g feces and <102-105 CFU/g feces, respectively. We also assessed the proportion of AMR bacteria in feces collected at 5, 12, 19, 26, 33, and 40 days of age from two flocks treated with amoxicillin at 5–7 days of age and co-trimoxazole at 24–26 days of age. The proportion of ampicillin (AMP)-resistant bacteria was elevated at 12 and 26-33 days of age on DHL containing 50 μg/mL AMP while no increase in LEX-resistant bacteria was observed on DHL-L. All isolates tested exhibited AMP resistance at 12 days of age while most exhibited resistance to both AMP and trimethoprim/sulfamethoxazole at 26-33 days of age. Our results suggested that antimicrobial administration influenced the selection of AMR bacteria with cross- and coresistance.
